1. Field of the Invention
The invention relates to a screw hole seal structure for sealing a screw hole in molding a fiber-reinforced resin member, in which an insert member having a screw hole is integrally incorporated, and also relates to a method of producing a fiber-reinforced resin member by using the screw hole seal structure.
2. Description of the Related Art
As a mount method of mounting a mounting member to a fiber-reinforced resin member, there is known a method in which a metal insert having a screw hole is incorporated integrally in a fiber-reinforced resin member, and the screw hole is used to mount a mounting member in the resin member.
In this method, if a fiber-reinforced resin member is molded with the screw hole of the metal insert exposed, the resin solution may enter the screw hole, so that the hardened resin may bury the thread of the screw hole. Therefore, it is a practice to adopt a method in which a block-shape metal insert is incorporated when a fiber-reinforced resin member is molded, and after the molding, a screw hole is formed in the metal insert.
Japanese Patent Publication No. 61-24971 shows a technology in which a mounting hole for a mounting bolt that is formed in a cavity block of a die molding apparatus is sealed with a seal member to block the entrance of the resin solution. The publication also shows as embodiments a method in which a push-in plug, which is a seal member, is freely removably fitted into a bolt hole to close the bolt hole, and a method in which a counterbore for the bolt head is provided with an internal thread portion, and a screw-in plug, which is a seal member, is screwed into the internal thread portion.
If oil adheres to a fiber-reinforced resin, the strength of the fiber-reinforced resin may decline. For example, when fiber-reinforced resin articles are adhered to each other by an adhesive, the adhesion may be inhibited, that is, the adhesion characteristic may be adversely affected.
Hence, in the above method of forming a screw hole in a metal insert after a fiber-reinforced resin member is molded, a wet process that uses cutting oil cannot be performed, and therefore a dry process that does not use the cutting oil needs to be performed. Compared with the wet process, the dry process requires a longer processing time, and therefore requires higher cost.
As a countermeasure, a method is conceivable in which a screw hole is formed in a metal insert beforehand by a wet process, and the screw hole is filled with silicone as a sealing material, and is hardened, and then the metal insert with the screw hole closed in this manner is incorporated integrally into a fiber-reinforced resin member by setting the insert in the mold of the fiber-reinforced resin member.
However, in the above method, the silicone charged in the screw hole may harden, interlocking with the screw thread, so that it may be difficult to remove the silicone from the screw hole, the removal operation is complicated, and may cause cost increase.
Furthermore, in the foregoing method, if the metal insert is incorporated in molding a fiber-reinforced resin member before the silicone completely hardens, the oil seeping from the silicone due to the hardening of the silicone may adhere to the fiber-reinforced resin, and may cause the problem mentioned above.
Therefore, the fiber-reinforced resin member cannot be molded until the silicone charged into the screw hole completely hardens. This may impede prompt operation, and may give rise to a problem of it being impossible to improve productivity.
In addition, it is also conceivable to adopt a method in which the screw hole is closed by a seal member, such as a push-in plug, a screw-in plug, etc., utilizing the technology described in Japanese Patent Publication No. 61-24971. However, the push-in plug is merely fitted in the screw hole in a state in which the plug is pressed due to its own elasticity within the screw hole. The screw-in plug is merely fitted by the external thread of the screw-in plug fastened into the internal thread of the screw hole.
Therefore, if a vacuum molding method is used, for example, a vacuum bag molding method, a Resin Transfer Molding (RTM) method, etc., to mold the fiber-reinforced resin member, the foregoing push-in plug or screw-in plug as a seal member may not be able to completely prevent entrance of the resin solution, but the resin solution that enters through a gap may harden to become a hardened resin burying the screw thread, depending on a condition, for example, regarding a place where the screw hole is formed within a molding die.